Relationship between strain accumulation and release associated with recent slow slip events on the Japanese Islands

Abstract

In this study, we investigated the relationship between the strain accumulation before a slow slip event (SSE) and the strain release during the SSE for three recent SSEs along the Suruga Trough, Sagami Trough, and Nankai Trough, which are subduction zones in central to southwest Japan. The three analysed SSEs were the 2013–2016 Tokai long-term SSE (L-SSE), the 2018 Boso-Oki short-term SSE (S-SSE), and the 2019–2021 Central Shikoku L-SSE. We applied exponential and logarithmic functions to remove the postseismic deformations caused by the Mw 9.0 2011 Tohoku-Oki earthquake. We discovered a strong negative correlation between strain accumulation and strain release in the dilatation of all three SSEs and in the maximum shear strain of the 2018 Boso-Oki S-SSE. A comparison of the amount of strain accumulation with that of strain release revealed that approximately 30% of the strain was released in the 2013–2016 Tokai L-SSE, that 40% of the strain was released in the 2019–2021 Central Shikoku L-SSE, and that approximately 60% of the strain was released in the 2018 Boso-Oki S-SSE. This finding suggests that all of the accumulated strains are not necessarily released by the SSEs.